Wireless communication has become common in all aspects of life today, whether it be a wireless home or office network, so-called “hotspot” networks at local cafes, fast food chains or hotels, or even citywide implementations of WiFi and other technologies. This desire to become a society of wireless communication has even extended to moving devices such as a moving vehicle. This type of wireless networking may appear in many aspects of vehicle safety applications, including, but not limited to, urgent road obstacle warning, intersection coordination, hidden driveway warning, lane-change or merging assistance.
Vehicle safety communications (“VSC”) may be broadly categorized into vehicle-to-vehicle and vehicle-with-infrastructure communications. In vehicle-to-vehicle communication, vehicles communicate with each other without support from a stationary infrastructure. Vehicles communicate with each other when they are within the same radio range of each other or when multiple-hop relay via other vehicles is possible. In vehicle-with-infrastructure communication, vehicles communicate with each other with the support of infrastructure such as roadside wireless access points. In this case, vehicles may also communicate with the infrastructure only.
Key VSC performance requirements include low latency (on the order of 100 milliseconds) and sustained throughput (or equivalently, the percentage of neighboring vehicles that successfully receive warning messages) in order to support various VSC applications such as collision avoidance. The '047 Application describes a method for organizing groups of moving vehicles into a Local Peer Group (LPG) by selecting one moving vehicle as a group header, maintaining the LPG using the group header, and generating local routing information. The LPG is formed by transmission of control messages such as heartbeats (HB) and membership reports (MR). The HB message has been implemented using flooding mechanisms. The moving vehicles are adapted for unicast and multicast routing.
However, packet distribution is a major overhead of LPG-based routing protocols including the unicast and multicast protocols. In situations where the number of neighbor nodes is large, such as in a traffic jam, duplicate packets significantly add to this overhead. Further, random contention among nodes induces considerable back-off time and then degrades link throughput, while there is high complexity of network coding in typical mobile ad-hoc networks. Accordingly, there is a need for efficient packet distribution.